The present invention generally relates to control circuits and disk units, and more particularly to a control circuit for controlling a disk unit and to a disk unit having such a control circuit.
Generally, a floppy disk drive has a control integrated circuit (IC) which receives signals from a host computer via an interface. This control IC controls operations of a spindle motor driving IC, a stepping motor driving IC, a recording and reproducing IC and the like depending on the states of the signals received from the host computer.
FIG. 1 is a timing chart for explaining the operation of a conceivable floppy disk drive.
A step signal ST shown in FIG. 1 is input from the host computer to the control IC. This step signal ST is used to drive a stepping motor. When this step signal ST is periodically input to the control IC, the control IC generates phase-A excitation pulses A.sub.1 which are inverted in synchronism with the rising edges of the step signal ST, and phase-B excitation pulses B.sub.1 which have a phase that lags the phase of the phase-A excitation pulses A.sub.1 by 90.degree..
The phase-A excitation pulses A.sub.1 and the phase-B excitation pulses B.sub.1 are input to the stepping motor driving IC and output via an output circuit. In addition, the phase-A excitation pulses A.sub.1 and the phase-B excitation pulses B.sub.1 are respectively inverted into inverted phase-A excitation pulses A.sub.2 and inverted phase-B excitation pulses B.sub.2 and output via the output circuit.
The phase-A excitation pulses A.sub.1 and the inverted phase-A excitation pulses A.sub.2 are applied across both ends of a first coil of the stepping motor to drive the same, while the B-phase excitation pulses B.sub.1 and the inverted phase-B excitation pulses B.sub.2 are applied across both ends of a second coil of the stepping motor to drive the same. As a result, the stepping motor is rotationally driven by excitation currents that flow to through the coils at predetermined timings.
When the stepping motor is driven, a head carriage mechanism having a recording and reproducing head on a tip end thereof is moved in a radial direction of a floppy disk, so as to carry out a seek operation in which a predetermined recording or reproducing position on the floppy disk is sought. A current I.sub.M consumed by the stepping motor during this seek operation has a waveform shown in FIG. 1. This current I.sub.M has an approximate rectangular waveform that periodically increases at 1/2 the period of the step signal ST.
The input of the step signal ST from the host computer to the control IC is stopped when stopping the seek operation. In this case, both the phase-A excitation pulses A.sub.1 and the phase-B excitation pulses B.sub.1 maintain a high level (that is, both the inverted phase-A excitation pulses A and the inverted phase-B excitation pulses B.sub.2 maintain a low level), and the stepping motor stops rotating, thereby carrying out a settling operation in which the head carriage mechanism is fixed to a predetermined position. Even during a settling time T.sub.s in which this settling operation is carried out, a high voltage signal HV that is input to the control IC and controls the excitation (ON/OFF) of the coils of the stepping motor is maintained at the high level. For this reason, an excitation current continue to flow through the coils of the stepping motor in a predetermined direction. As a result, the current I.sub.M consumed by the stepping motor during this settling operation greatly increases to a predetermined value as shown in FIG. 1.
Therefore, according to the conceivable floppy disk drive described above, there is a problem in that the power consumption is large because the current I.sub.M consumed by the stepping motor during the seek operation of the head carriage mechanism periodically increases, and this current I.sub.M greatly increases to the predetermined value during the settling operation.